Leo - Aug 10 to Sep 16 (July 23 to August 22) Gemini - Jun 21 to Jul 20 (May 22 to June 22)Ĭancer - Jul 20 to Aug 10 (June 23 to July 22) Taurus - May 13 to Jun 21 (April 21 to May 21) Pisces - Mar 11 to Apr 18 (Feb 21 to March 19)Īries - Apr 18 to May 13 (March 20 to April 20) What's your "real" zodiac sign?īelow are the dates that a truly astronomy-based zodiac would give each astrological sign, while the dates that the astrology-based system devised two millennia ago are given in brackets.Ĭapricorn - Jan 20 to Feb 16 (Dec 23 to Jan 21)Īquarius - Feb 16 to Mar 11 (Jan 22 to Feb 20) The ancient stories of the Babylonians' - who are often credited with originating astrology - acknowledge there were 13 constellations in the zodiac, but Ophiuchus was chosen to be left out. Astrologers actually ignore the 13th constellation on the ecliptic - Ophiuchus - instead, sticking to the 12-sign zodiac. There's another problem with the zodiac as astrologers see it and the position of the sun along the elliptic. That means if the founders of the zodiac had been aware of precession, she'd have been an Aries rather than going through her whole life as a Taurus. So taking 2010 as an example - an 'average year' slotted between two leap years - a child born on April 26, 2010, will be a Taurus despite the fact the sun was actually in the constellation Aries on that day and wouldn't move into Taurus until May 14. As result zodiac signs no longer align with the position of the sun.įor example, the astrological sign Taurus is said to govern the period between April 20 and May 20, as that's the constellation that the sun once appeared to be in during this period. That means that each period now occurs about one-tenth of a year - roughly a month - later than it did when astrology was being devised.īut horoscopes published in papers and magazines don't follow this astronomical system. For this reason, it is often called the precession of the equinoxes.Īs a result, the astrological signs have also shifted one-tenth around the elliptic to the west in relation to the background stars. Precession has also had the effect of shifting the equinoxes of Earth - the two points of the year at which day and night have equal lengths - along the ecliptic. Over the last 2,500 years, the intersection of the celestial equator and the ecliptic has drifted west along the ecliptic by 36 degrees - about one-tenth of its length.Īn illustration showing Earth's wobble along its rotational axis. This means that the North Pole isn't always pointing in the same direction as the background stars of the celestial sphere, and this effect accumulates. Watching this pole over the course of 25,800 years, we would see it trace out a circle over the Earth. To picture this precession, imagine a literal pole extending out of Earth at the North Pole. Known as precession this 'wobble' has a 25,800-year cycle. ![]() The gravity of the moon and the sun, and to a lesser extent the planets, acts on Earth's equatorial bulge - caused by the planet's rotation - to shift its axis of rotation. The cause of the shifting in zodiac signs is precession, the slight 'wobble' Earth experiences as it orbits the sun. The problem was, that these ancient astrologers weren't aware of a ' wobble' in Earth's motion that would seriously disrupt their system as time progressed. The other astrological signs of the zodiac were categorized in a similar way, each grabbing its own 30-degree slice of the ecliptic. This intersection is also known as the vernal equinox and the spring equinox in the Northern Hemisphere because it is considered the first day of spring.Ģ,200 years ago this zero point occurred in Aries, hence its name the "first point of Aries." As a result, Aries the constellation occupied the first 30 degrees of the ecliptic from 30 to 60 degrees was taken by Taurus, and Gemini was positioned from 60 to 90 degrees. The zodiac was initially developed around 600 BCE and its zero point was defined as the point that the ecliptic intersected with the celestial equator - the great circle of the terrestrial equator on the celestial sphere. (Image credit: Wikimedia commons/Tauʻolunga) An illustration of the sun's motion relative to Earth throughout the year as it crosses in front of constellations representing the astrological signs of the zodiac.
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